Competing model formulations
| Model | Normalized force: | Normalized recruitment term: | Normalized distortion term: | Second order terms: | No. of parameters: |
| φ(t) = | |||||
| I | ε(t)ζ(t) | — | Three: b and c (with units of s−1) and υ0 (unit-less) | ||
| II | ε(t)ζ(t) | — | Four: b, γ, and c (with units of s−1) and υ0 (unit-less) | ||
| III | ε(t)ζ(t) | — | Four: b and c (with units of s−1) and γ and υ0 (unit-less) | ||
| IV | ε(t)ζ(t) | — | Five: b and c (with units of s−1) and γn, γx, and υ0 (unit-less) | ||
| V | ε(t)[ζ(t) + κζ1(t)] | Six: b, γ, c, and d (with units of s-−1) and κ and υ0 (unit-less) | |||
| VI | ε(t)ζ(t) | Six: b, γ, c, and a (with units of s−1) and θ and υ0 (unit-less) |
| Model | Normalized force: | Normalized recruitment term: | Normalized distortion term: | Second order terms: | No. of parameters: |
| φ(t) = | |||||
| I | ε(t)ζ(t) | — | Three: b and c (with units of s−1) and υ0 (unit-less) | ||
| II | ε(t)ζ(t) | — | Four: b, γ, and c (with units of s−1) and υ0 (unit-less) | ||
| III | ε(t)ζ(t) | — | Four: b and c (with units of s−1) and γ and υ0 (unit-less) | ||
| IV | ε(t)ζ(t) | — | Five: b and c (with units of s−1) and γn, γx, and υ0 (unit-less) | ||
| V | ε(t)[ζ(t) + κζ1(t)] | Six: b, γ, c, and d (with units of s-−1) and κ and υ0 (unit-less) | |||
| VI | ε(t)ζ(t) | Six: b, γ, c, and a (with units of s−1) and θ and υ0 (unit-less) |
Model legend: I, simple RD model; II, RD model with nonlinear interaction term (NLRD model); III, NLRD model with nonlinear distortion effect on distortion (same nonlinear effect of distortion on both recruitment and distortion); IV, NLRD model with nonlinear distortion effect on distortion (same nonlinear effect of distortion on both recruitment and distortion); V, NLRD model with second-order distortion term; VI, NLRD model with second-order recruitment term.